In production of photographic light-sensitive materials, it is normal that a photographic light-sensitive material is slit to a predetermined width, wound around a core for a specified length to form a roll which is covered with a light-shielding material.
It is ideal that this photographic light-sensitive material in a roll shape is wound evenly and tightly from the start of winding up to the end of winding as far as possible from the viewpoint of storage conditions, distribution conditions and easy handling.
However, this photographic light-sensitive material in a roll shape has a step whose height corresponds to the thickness of the photographic light-sensitive material near the core. The step causes high concentrated pressure when trying to wind up tightly, resulting in a protruded deformation (press mark) and sensitivity abnormality on the photographic light-sensitive material near the core.
Due to the abnormality mentioned above, it has been impossible to use about 20% of photographic light-sensitive materials which are expensive.
Therefore, the proposals described below have been made.
For example, Japanese Patent Publication Open to Public Inspection Nos. 165861/1984 and 164275/1987 (hereinafter referred to as Japanese Patent O.P.I. Publication), Japanese Patent Examined Publication No. 24116/1990, Japanese Patent O.P.I. Publication Nos. 142941/1989 and 116882/1990 disclose technology wherein a conventional core has been improved in a way that a buffer layer is provided for preventing an influence of a step on the end of a photographic light-sensitive material. Elastic adhesives, resin foaming substances and paper or synthetic paper having low density are used as a material of the buffer layer. Further, for example, technology, wherein the same effect as in the above is achieved by providing a cutout on the external surface of the core without providing a buffer layer, is disclosed in Japanese Patent O.P.I. Publication Nos. 14072/1988, 8689/1991 and 8690/1991.
It has been effective, as a core around which a photographic light-sensitive material is wound, to provide a buffer layer for preventing deformation (press mark) and abnormality of sensitivity caused by pressure caused on a photographic light-sensitive material near the core. However, resin materials, various rubber or elastic adhesives glued on the core have deteriorated the core, after the core becomes waste, on the points of disposability and reusability.
Namely, substances used as these buffer materials do not decompose spontaneously when disposed as waste, for example, and even when they are subjected to incineration, they produce a toxic gas which damages an incinerator together with high temperature therein.
When recycled, the abovementioned buffer layer needs to be removed, which is time-consuming. Actually, however, some of the buffer layers are glued firmly and can not be removed.
With regard to disposal of waste, each country has its own law, and in Europe, in particular, it is required that a single kind of material is used. Therefore these cores do not comply with the law.
Even when a nonwoven fabric is used as a material having a buffer effect, the unwoven fabric is usually made of various synthetic fibers such as nylon, rayon and polyester or the like for the purpose of an improvement of its strength, or these synthetic fibers are generally mixed with pulp at a rate of about 20%-60%.
These synthetic fibers are problematic from the viewpoints of disposability and adaptability for recycling. When they are of a single material without reinforcement, which is ideal for improvement in disposability and adaptability for recycling, the strength thereof becomes too low to be processed as a core.
For the processing of a core, for example, a material of a core is required to have tensile strength of 0.3 kg/15 mm or more. A dry unwoven fabric made of a single material of pulp has tensile strength of 0.3-0.6 kg/15 mm when dry, while 15 times foamed polystyrene known in the conventional example has that of about 6 kg/15 mm. When adhesives are coated on the unwoven fabric for pasting it on the core, however, tensile strength of the unwoven fabric falls sharply to 0.1-0.3 kg/15 mm due to its wet state, preventing it from being wound round the core.
In the method of providing a cutout on the external surface of a core, on the other hand, an end of a light-sensitive material needs to be positioned accurately to engage with the cutout in a dark room. Therefore, complicated equipment and reduction of efficiency caused by increased working hours can not be avoided.
On the other hand, a slitter wherein the core is used has recently been highly automated and complicated and productivity has been steeply enhanced. However, a core to be used therein has actually been required to have higher dimensional accuracy.
Heretofore, however, attention has been paid only to an influence of moisture and oxidation-reduction substances contained in the core on a photographic light-sensitive material. Therefore, the core, after being cut to the predetermined dimensions, has been stored in a cardboard box packaging, and immediately before it is used, it has been subjected to a drying process under predetermined conditions of temperature and time, for example, 50.degree. C. and 24 hours to be adjusted to 8% or less in terms of moisture content.
In the above occasion, the core has been cut to dimensions wherein a constant percentage of shrinkage of the core is considered so that the core may have predetermined dimensions after drying, because the width of the core shrinks after the drying process. However, it has been impossible to satisfy the required dimensional accuracy, due to dimensional dispersion in the process for cutting a core and dispersion in the progress of drying caused by the difference of taken-in moisture such as, for example, the difference between positions in cardboard box packaging such as upper, middle or lower position or the difference between seasons.
For further improvement of dimensional accuracy, there have been taken various methods such as control of moisture content in a core material, change of cutting dimensions for each season and calculation of design value for each time based on a shrinkage factor by moisture content. However, all of them have required extremely complicated moisture content control and calculation, inventory control and work. Therefore, they proved to be difficult to carry out and failed to be a basic solution, resulting in equipment problems and complaints from customers.